Neutrino factories based on muon decay rings

Using muons as a source of neutrinos can be traced back to 25 years ago but it is with the recent studies on muon colliders that this idea came back to the front of the stage. It was specifically discussed in a FNAL workshop (1997), a BNL workshop (1998) and a study group dedicated to that topic was set up at CERN in 1998. νFact99 appears as the conclusion of this preparatory work and is the first international workshop on neutrino beams produced by the decay of muons in a storage ring. It was co-sponsored by ICFA and ECFA and attended by 120 participants. Proceedings will be published. Physics and accelerator issues were discussed on the same footing. The main physics issue was the theory and detection of neutrino oscillations within the context of three or more families. On the accelerator side, three scenarios have been investigated and finally harmonized in a single conceptual design. Last, topics needing R&D are mentioned.